I posted 13 shows in this thread comparing my mk41>VMS02IB>70d and mk4>PFA>70d setups so that you can hear the two different preamps and compare the 70d pres to the VMS pres
I realize that the caps/KCY's are different, but this should give you a good idea what the stock 70d preamps sound like! I agree that the recorder gets blamed a lot for pulling bad recordings, when it was really mic placement/venue sound/mic choice/etc! You put good in, you get good out, as for most things
I think the 70d pres are more than adequate for most mics and types of recording! If you need tons of gain, like Voltronic has pointed out, then you probably need a HQ external pre, but for most types of music, the pres should be more than enough! As always, YMMV.
http://taperssection.com/index.php?topic=177215.msg2184452#msg2184452